The regulation of gene expression in bacteriophage-infected E. coli is being studied by analysis of the size, function and stability of specific mRNAs. mRNA is assayed by protein synthesis in vitro followed by analysis of the proteins synthesized by SDS-polyacrylamide slab gel electrophoresis. Polycistronic mRNAs during T4 and T7 infection are being studied using these techniques in combination with preparative polyacrylamide gel electrophoresis to fractionate mRNAs on the basis of MW and conformation. The regulation of translation of T7 mRNA and T7-infected male E. coli strains is also under investigation.